Odontochilus putaoensis, a new species of Orchidaceae, is described and illustrated from Putao Township, Kachin State, Myanmar. Odontochilus putaoensis is close to O. duplex, but can be easily distinguished from the latter by having a light yellow lip, a bisaccate hypochile with a small, erect, blade-like and emarginate callus within each sac, a mesochile with a pair of dentate-pectinate flanges and a bilobed epichile with a pair of widely diverging lobes that are erect and concave. An identification key to the Southeast Asian species of Odontochilus and colour photographs of O. putaoensis are provided. A preliminary conservation assessment according to the IUCN Red List Categories and Criteria is given for the new species.

Cranichideae , Kachin State, key, new species, southeast Asia, terrestrial orchid

Odontochilus Blume (1858) (Orchidaceae, Orchidoideae, Cranichideae) consists of approximately 40 species, distributed from tropical Asia, Pacific islands to Japan, subtropical mainland Asia and eastern Himalayas (Pridgeon et al. 2003, Chen et al. 2009, Pedersen et al. 2011, Chase et al. 2015, Tang et al. 2016). Most species of Odontochilus are small terrestrial plants, usually found in humid evergreen broadleaved forests. The generic delimitation of Odontochilus has been confused for a long time with its relative Anoectochilus Blume (1825). As both genera share some floral characters such as pectinate mesochile, ventral column wings and two stigma lobes, they were usually considered as one genus (Lang 1999, Pridgeon et al. 2003). Morphologically, Odontochilus is distinguished from Anoectochilus by its saccate and non-extruded spur enclosed by the lateral sepals and two parallel stigma lobes positioned under the rostellum, whereas Anoectochilus has a conical spur extruded beyond the lateral sepals and two remote stigma lobes (Lin and Hsu 1976, Pridgeon et al. 2003, Chen et al. 2009, Pedersen et al. 2011). Recent results of molecular systematics indicated that Odontochilus is closely related to Chamaegastrodia and Rhomboda, whereas Anoectochilus is closely related to Ludisia (Li et al. 2016).

In the continental part of southeast Asia, there are nine species of Odontochilus (Seidenfaden 1992, Schuiteman et al. 2008, Chen et al. 2009, Pedersen et al. 2011, Kurzweil and Lwin 2014, Averyanov et al. 2015, Tang et al. 2016). Although there is no recorded species of Odontochilus in the checklist of Kress et al. (2003), there are several species listed as occurring in Myanmar in the floristic documents of Chen et al. (2009), Pedersen et al. (2011) and Kurzweil and Lwin (2014). During our fieldwork in Putao Township, Kachin State, northern Myanmar, in October 2014, a new species of Odontochilus was discovered and is described below.

All measurements of the new Odontochilus species were taken from dried herbarium specimens and field notes. In the description, length and width are represented as length × width. In total, four living plants and one dried specimen of the new species were examined. All measurements of O. duplex (Holttum) Ormerod (Peninsular Thailand and Peninsular Malaysia) were based on literature (Seidenfaden and Wood 1992, Ormerod 2005, Pedersen et al. 2011).

Myanmar lies in southeast Asia and is well endowed with biodiversity-rich areas such as tropical evergreen rainforest, coastal mangrove forest and subtropical montane forest. The northern part of Myanmar is situated in the ecological transition area of three global biodiversity hotspots, the Indo-Burma hotspot, Mountains of southwest China hotspot and Himalaya hotspot (Myers et al. 2000, Sodhi et al. 2004, Mittermeier et al. 2011, Khine et al. 2017, Jin et al. 2018). However, the biodiversity of northern Myanmar is far less understood due to the absence of scientific research. Recently, biodiversity research activities in northern Myanmar have been jointly conducted in cooperation with international research institutions, resulting in discoveries of new species of fauna and flora, such as Aristolochia sinoburmanica Y.H.Tan & B.Yang, Bulbophyllum putaoensis Q.Liu, Coelogyne putaoensis X.H.Jin, L.A.Ye & Schuit, Gastrodia kachinensis X.H.Jin & L.A.Ye, G. putaoensis X.H.Jin, Hedychium putaoense Y.H.Tan & H.B.Ding, Kerivoula kachinensis, Muntiacus putaoensis, Oreoglanis hponkanensis, Rhinopithecus strykeri, Selliguea kachinensis Hovenkamp, S.Linds. & Fraser-Jenk. and so on (Amato et al. 1999, Bates et al. 2004, Geissmann et al. 2011, Khine et al. 2016, Aung et al. 2017, Chen et al. 2017, Jin and Kyaw 2017, Liu et al. 2017, Aung and Jin 2018, Ding et al. 2018, Yang et al. 2018).

Odontochilus putaoensis is a very distinctive species in having easily identifiable floral features such as a pair of erect and concave epichile lobes. Having such distinctive floral features, O. putaoensis can be easily distinguished from its closely related species, O. duplex, although both species are more or less similar in their vegetative as well as floral characters. In addition, their altitudinal range and habitat type are relatively comparable: O. putaoensis was collected at 1500–2000 m elevation and O. duplex at ca. 750 m elevation (Pedersen et al. 2011). Odontochilus putaoensis grows in subtropical broad-leaved, evergreen forest in northern Myanmar, whereas O. duplex in the upper tropical rainforest in Peninsular Thailand and Peninsular Malaysia (Pedersen et al. 2011). As well, O. putaoensis flowers in October while O. duplex in May (Pedersen et al. 2011).

Special thanks are due to Vincent Droissart for his critical and helpful comments and suggestions on the manuscript. We also acknowledge Hubert Kurzweil for the substantial corrections/modifications he made during the first round review. This research was supported by grants from the Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (Grant No. Y4ZK111B01) and the National Natural Science Foundation of China (Grant Nos. 31670194, 31620103902).